Solar Panel Charge Time Calculator (Australia)

How to use this calculator

Enter six values and the calculator returns charge time in hours and days plus a verdict on whether your array is sized correctly:

1. Battery capacity (Ah) — printed on the case. A typical Australian 4WD dual-battery setup is 100–120 Ah AGM; a Coromal or Jayco caravan is 100–200 Ah; an off-grid station bank can be 400–1,500 Ah.
2. Battery voltage — 12 V for vehicles and small caravan systems, 24 V or 48 V for sheds and off-grid homesteads.
3. Depth of discharge (%) — how empty the battery currently is. 50% is the standard lead-acid daily target; LiFePO₄ tolerates 80–100%.
4. Panel total wattage — sum of every panel’s STC rating (e.g. four 200 W panels on a caravan roof = 800 W).
5. Peak sun hours per day — for your location and season (see the FAQ for state-by-state averages).
6. System efficiency (%) — leave at 75% unless you have a clean MPPT plus LiFePO₄ setup, in which case 85% is reasonable.

The formula

The calculator uses the energy-balance equation that AS/NZS 4509.2 and every CEC-accredited stand-alone designer applies:

energyNeeded (Wh) = batteryAh × batteryV × (depthOfDischarge / 100)
dailyEnergy (Wh)  = panelW × peakSunHours × (efficiency / 100)
days              = energyNeeded / dailyEnergy

A worked example for a typical Aussie caravan setup heading up to Cape York:

• 200 Ah × 12 V × 0.50 = 1,200 Wh to recover from 50% DoD
• 400 W × 5.5 h × 0.75 = 1,650 Wh delivered per day
• 1,200 ÷ 1,650 = 0.7 day (under 4 hours of peak sun)

And for a Victorian off-grid weekender in winter:

• 600 Ah × 24 V × 0.60 = 8,640 Wh to recover from 60% DoD
• 1,200 W × 2.6 h × 0.75 = 2,340 Wh delivered per Melbourne winter day
• 8,640 ÷ 2,340 = 3.7 days of clear winter sun

Charge time reference table (Australia)

Common scenarios using 5.0 peak sun hours (national average) and 75% system efficiency, starting from 50% depth of discharge:

Multiply charge time by 1.5 for typical Sydney winter, 2.0 for Melbourne winter, 2.3 for Hobart winter. Northern Australia (Darwin, Cairns, Broome) barely changes seasonally.

Common Australian scenarios

Caravan and camper trailer (Big Lap touring)

A 200–400 W roof array and a 100–200 Ah AGM or 100 Ah lithium battery is the standard configuration sold by Caravan World and TJM dealers. With a 50% nightly draw from a Waeco fridge plus lighting, 200 W just keeps pace in winter Victoria; 400 W gives comfortable headroom anywhere except southern Tasmania in July.

4WD dual-battery (overlanding)

100–120 Ah aux battery under the bonnet or in a drawer system, 80–160 W of solar via a Redarc DC-DC controller. Recovery time matters less because the alternator handles bulk charging while driving — the panel only tops up during stationary camp days. Use the calculator to confirm 24-hour stationary loads are covered.

Off-grid homestead (rural NSW, Vic, Tas)

48 V system voltage, 600+ Ah lithium battery, 6–10 kW of panels and MPPT charge controllers (Victron or Selectronic). At this scale you size for one-day recovery in worst-case (June/July) conditions, which means substantial summer overproduction — often diverted to hot water via Catch Power or similar diverters. See the solar wire size calculator for the long ground-mount-to-shed runs typical at this scale.

Outback station and remote telecoms

Sized for 5–10 days of autonomy because clear sun is reliable but maintenance access isn’t. A typical Telstra remote tower runs 1–2 kW of panels, 1,200–2,000 Ah at 48 V, and minimal generator backup. The CEC stand-alone design guidelines specify these autonomy figures for sites more than 100 km from the grid.

What the calculator deliberately ignores

• Solar irradiance variation across the day. Real production curves are a bell shape. The “peak sun hours” abstraction handles this for energy totals — but if your charge controller can’t accept the midday peak current (undersized for array Imp), you’ll lose more than the 75% default suggests.
• Battery state-of-charge taper. The last 10–20% of a lead-acid charge cycle takes the same time as the first 80%. The calculator models the bulk phase only — add 1–2 hours for absorption and float.
• Charge-rate limits. Lithium accepts up to 1 C (a 100 Ah battery takes 100 A). Lead-acid is typically 0.1–0.2 C. If your array delivers more than the battery accepts, the surplus is wasted.
• Australian summer heat derating. A panel rated at 25°C produces about 18% less when its cells hit 70°C — common on a black-roofed Queenslander in February. Dual-axis tilt or rear-ventilated mounts mitigate this.

Sizing rule of thumb (Australia)

If you want one-day recovery from a normal night’s discharge:

• Panel watts ≈ Battery Wh × 0.5 — northern Australia (Darwin, Cairns, Broome): 5.5+ peak sun hours
• Panel watts ≈ Battery Wh × 0.55 — capital cities annual average: 4.5–5 peak sun hours
• Panel watts ≈ Battery Wh × 1.0 — southern winter (Melbourne, Hobart, Adelaide June–August): 2.5–3 peak sun hours

For dependable off-grid power across Australian weather, multiply panel watts by a further 1.5–2× to handle 2–3 cloudy days. The CEC Stand-alone Power System Design Guidelines specify minimum 3-day autonomy for unattended sites.

Cost context (Australia 2026)

Typical equipment pricing in 2026 from Battery World, Jaycar and Solar 4 RVs:

• 100W mono panel + PWM controller + AGM 100Ah battery: AUD $450–$650
• 200W panel + 20A Victron MPPT + 100Ah lithium: AUD $1,400–$1,800
• Off-grid 5 kW array + 10 kWh lithium + Selectronic inverter, installed: AUD $25,000–$38,000 (CEC-accredited installer, 2026 average via SunWiz)

Compare quotes through Service.com.au or hipages — at least three CEC-accredited quotes, since the spread between cheapest and dearest is often 30% on the same equipment list.

Sources

• Clean Energy Council — Stand-alone Power System Design Guidelines — Australian off-grid sizing benchmarks
• AS/NZS 4509.2:2010 — Stand-alone power systems design
• Bureau of Meteorology Solar Radiation — peak sun hours by location
• SunWiz Australian PV Market Report — 2026 install cost data